Method of Imparting Reduced Ignition Propensity to Smoking Articles Using Phase Transition Materials

ABSTRACT

A method for imparting reduced ignition propensity properties to a smoking article by treating the smoking article wrapper with a phase transition substance which, upon being subjected to the heat of the smoking article burning firecone, physically transforms and at least partially fills the pores of the smoking article wrapper to reduce the permeability of the wrapper in the vicinity of the burning firecone. The reduced permeability of the wrapper in the vicinity of the firecone will permit sufficient air flow to sustain free burn, but, when the smoking article is placed on a substrate, the reduced permeability of the wrapper imparts reduced ignition propensity such that there is insufficient air flow to sustain combustion of the firecone or insufficient air flow to sustain an intensity of the burning firecone necessary to ignite the substrate.

This application claims priority to U.S. application Ser. No. 61/449,280 file Mar. 4, 2011, U.S. application Ser. No. 61/449,299 file Mar. 4, 2011 and U.S. application Ser. No. 61/450,375 filed Mar. 8, 2011, the entire contents of each of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to a method for providing a smoking article with reduced ignition propensity (IP) properties, and more particularly, a method of applying, treating, coating, integrating or disbursing a phase transition material on or in the smoking article wrapper to provide a smoking article with acceptable free burn properties when in a static state and acceptable reduced IP properties when in contact with a substrate.

BACKGROUND

Under some circumstances smoking article (e.g., cigarettes) may ignite fire-prone substrates if the article is accidentally laid on or put in contact with a substrate. Therefore, a cigarette prepared from a wrapper, which diminishes the ability of the cigarette to ignite a substrate, may have the desirable effect of reducing the cigarette-initiated fires. Furthermore, a wrapper that concurrently confers on a cigarette ability to free burn (FB) in a static state and reduction in the tendency of the article to ignite fire-prone substrates, maintains and improves consumer acceptability, including the product appearance before, during and after use. Moreover, it is important that the construction of the cigarette exhibits a sufficiently long shelf-life while maintaining improved IP and FB characteristics.

Cigarettes claiming to possess reduced ignition propensity and ability to free burn in the free-held state are commercially available. Nonetheless, the focus of ongoing industry research with respect to the ignition propensity has been directed to the: (1) fundamental understanding of mechanisms of cigarette combustion and ignition of substrates; (2) new technologies that could be useful in designs for further reducing the cigarette ignition propensity; (3) improvement in manufacturing and quality assurance while producing the reduced ignition propensity cigarettes; (4) improvements in monitoring the parameters of reduced ignition propensity performance; and (5) consumer satisfaction and other non-safety-related commercial concerns. Since the effectiveness of existing standards for reducing the fires and fire losses has yet to be determined based on population data, and the new advances in ignition propensity research can potentially lead to less ignition-prone cigarettes than those on the market, an improvement of the reduced IP technology is still necessary and is disclosed herein.

Critical to the success of new technologies for imparting cigarettes with reduced ignition propensity is a further improvement to reliability and effectiveness. It is known that cigarettes with excellent reduced ignition propensity are prone to diminish customer satisfaction because they tend to self-extinguish while the smokers hold them free in their hands. A measure of a cigarette's combined reduced ignition propensity and free burn characteristics is referred to herein as the LIP index, which is the product of the free burn success rate FB and reduced ignition propensity success rate IP. In the current starch-banded reduced IP products, that LIP index (IP×FB) could be as low as 80% for some products. In other words, 80% of the time so-called fire-safe cigarettes meet both free burn and reduced ignition propensity success. It will be understood that the LIP index is calculated based on the FB and reduced IP performance characteristics of a sample population of at least 10 cigarettes, and preferably a sample population of 20 or 40 cigarettes.

The present invention addresses the need for robust customer satisfaction in terms of the LIP index, appearance and quality of smoke, while exceeding the current self-extinguishing cigarette rate. The last parameter characterizes the time the cigarette stays smoldering on substrate before it goes out. This rate is a direct measure of the fire safety of cigarette. The present invention is directed to a reduced ignition propensity smoking article with a LIP index of at least 90% without detrimentally altering the taste perception and with an improved robustness in comparison with the current starch-banded product.

In addition, the current starch-banded technology of the LIP smoking article requires a conversion of the base paper to its LIP state prior to the cigarette manufacturing at the maker, which leads to an additional conversion costs. The new technology according to the disclosed invention enables LIP treatment done to the paper at the cigarette making machine. Thus, there remains a need for a new and improved wrapper and smoking article having reduced ignition propensity while at the same time possessing a sufficient probability of free burn.

SUMMARY OF THE INVENTION

The present invention is directed to a smoking article having improved LIP index. The smoking article includes a tobacco column, a wrapper having a porosity which provides sufficient gas permeability and, optionally, a filter element. A phase transition material is applied to, treated or integrated with or deposited, coated or disbursed on the wrapper in a patterned or non-continuous manner and in a sufficient amount to alter the porosity or gas permeability of the wrapper upon heat-induced phase transition. Without wishing to be bound by any scientific theory and explanation, applicants believe that, upon heat-induced phase transition, the phase transition material interacts with the wrapper in a number of ways. For example, it is believed that the phase transition material diffuses, merges, solidifies and blocks the wrapper pores to restrict air flow or transfer through the wrapper to the burning firecone. The restricted air flow will be sufficient to sustain free burn in a static state. However, when the smoking article contacts a substrate, the substrate further restricts the air flow to the burning firecone such that there will be an insufficient amount of air flow to sustain the combustion of the firecone or sustain sufficient intensity of combustion of the firecone to enable ignition of the substrate. In addition, it is believed that, when the smoking article is laid on or placed in contact with a substrate, the phase transition material creates a heat insulator between the burning firecone and the substrate. Overall, the phase transition material interacts with the wrapper in a manner such that the burning tobacco firecone self-extinguishes or tends not to ignite a substrate if the smoking article is left in contact with the substrate.

The composition of the phase transition material may comprise an individual phase transition material such as paraffin, tobacco wax, Solanesol, carnauba, Beeswax, microcrystalline wax, etc. or combinations thereof. The phase transition material may further comprise liquid crystal types of materials.

The tendency of a cigarette to self-extinguish or not ignite an ignitable substrate can be measured by ignition propensity tests such as those published by the Consumer Products Safety Commission and developed by the National Institute of Standards and Technology (NIST) or the American Society of Testing and Materials (ASTM). See Ohlemiller, T. J. et al., “Test Methods for Quantifying the Propensity of Cigarettes to Ignite Soft Furnishings. Volume 2, “NIST SP 851; volume 2; 166 pages [also includes: Cigarette Extinction Test Method, see pp. 153-160] August 1993 available from U.S. Consumer Product Safety Commission, Washington, D.C. 20207 as order number PB94-108644, the subject matter of which is herein incorporated by reference. One NIST ignition propensity test, the “cotton duck test”, involves placing a smoldering cigarette on a test assembly composed of a cellulosic Cotton Duck 6 or 10 fabrics over a foam block. Variations of the test use fabrics of various weights and polyethylene sheet backing A test failure occurs when the fabric ignites. Another NIST test, the “filter paper test”, involves placing a smoldering cigarette on a test assembly composed of layered filter paper sheets. Various forms of the test use 3, 10, and 15 layered filter paper sheets and a specified air velocity around smoking article. A successful test result occurs when the cigarette self extinguishes before the whole tobacco column is consumed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood after a reading of the following description of the preferred embodiments when considered with the drawings in which:

FIG. 1 is a chart comparing the LIP index of commercial LIP cigarettes having fixed starch bands available from 2005-2010 with LIP cigarettes embodying the transient band technology of the present invention;

FIG. 2A is a chart comparing the air permeability of the base paper and the starch-banded regions of commercial LIP cigarettes with the air permeability of the cigarette wrapper of the present invention treated with a patterned or uniform, non-continuous application of PTM;

FIG. 2B is a schematic illustrating configurations of the commercial fixed starch band LIP cigarette and a cigarette embodying the present invention having a wrapper treated with a patterned or uniform, non-continuous application of PTM;

FIG. 3A is a schematic of a cigarette embodying the present invention, which demonstrates how the PTM in conjunction with the cigarette firecone forms a transient band of decreased air permeability at the distal region of the cigarette;

FIG. 3B is a graph illustrating the air permeability of 70 C.U. paper treated with varying % weight treatments of paraffin;

FIG. 4A is a graph illustrating the pore volume distribution of 19 C.U. and 32 C.U. paper treated with 5% PTM according to the present invention;

FIG. 4B is a graph illustrating the reduction of the pore volume distribution of 19 C.U. and 32 C.U. paper treated with 5% PTM according to the present invention after being heated at 130° C. for 10 minutes;

FIG. 5A is a chart illustrating the effect of PTM concentrations according to the present invention with regard to the total pore volume of 0.5 μm and 5.0 μm pores as measured by mercury porosimetry;

FIG. 5B is a chart illustrating the reduction of .0.5 μm and 5.0 μm pore size regimes post thermal treatment according to the present invention;

FIG. 6 is a chart demonstrating the impact of the PTM deposition technology on the smoking article LIP properties;

FIG. 7 is a chart comparing the length of smoking article consumed before self-extinguishing for commercial reduced IP cigarettes having fixed starch bands and cigarettes having a 19 C.U. and 32 C.U. wrapper treated with a uniform, non-continuous application of PTM, as well as a standard deviation around this length; and

FIG. 8 is a graph illustrating the relative decrease in porosity of 19 C.U. and 32 C.U. cigarette paper with increased concentrations of PTM.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in general, it will be understood that the illustrations are for the purpose of describing preferred embodiments of the invention and are not intended to limit the invention thereto.

Exemplary smoking articles embodying the present invention may comprise tobacco blend, wrapped in an air-permeable paper of 10-100 Coresta Units, wherein the wrapper has been modified or treated with 0.5-35 weight % of Phase Transition Material (PTM) having melting temperatures within the range of 50-250° C. The PTM may comprise a single material or a composition of materials. Further, the PTM may be applied to the inner and/or external surface of the wrapper, or embedded in the wrapper pore structure. Smoking articles according to the present invention self-extinguish when placed on substrate and continue to free burn when suspended in the air and not touching other surfaces, manifesting the property of Low Ignition Propensity (LIP) characterized by an overall LIP index of 90% and higher.

In the present invention, applicants have found that phase transition materials such as paraffin, carnauba, other PTMs (e.g., Beeswax, microcrystalline wax, tobacco wax, Solanesol, etc.) and liquid crystal type materials impart improved IP characteristics to cigarette papers when the phase transition material is applied as a non-continuous, uniform layer on the surface of the cigarette paper in sufficient amount to alter the gas permeability of the paper upon phase transition (e.g., melting, etc.). In this manner, the non-continuous PTM layer in the vicinity of the firecone undergoes a phase change (e.g., melts) and wicks through the port net of the wrapper to form a circumferential band having reduced gas permeability compared to the gas permeability of the wrapper prior to the phase change of the PTM.

Applicants have found that machine-made cigarettes embodying the present invention demonstrate that about 5% to 35% of individual PTMs or combinations thereof (e.g., heterogeneous mixtures forming the non-continuous layer or coating on the paper) is effective to achieve a 100% reduced ignition propensity performance and a 100% free burn performance of the smoking article.

Applicants have also found that the overall PTM content can be minimized by selecting PTMs that favorably interact with each other and the paper upon initial disposition, as well as melting upon being subjected to the heat of the burning firecone and subsequently solidifying to form a circumferential banded region of reduced gas permeability. Phase transition materials are understood to be materials that undergo phase changes when an intensive variable, e.g., temperature or pressure, change. Exemplary phase transitions include eutectic, peritectic, spinodal and other physical transformations, where transitions are driven by an intensive variable changes, but are predominantly those that possess a solid to liquid transition upon heating.

Applicants have found that the LIP index, which is a quantitative measure of both the free burn and reduced ignition propensity success rates (IP×FB=LIP index), for tested samples of cigarettes embodying the present invention exceeded 95% and was consistently higher than the 80% LIP index for the currently commercial fixed starch-banded LIP cigarettes. The improvement in the ignition propensity and free burn performance of embodiments of the present invention compared to commercial fixed starch-band reduced ignition propensity cigarettes is illustrated in FIG. 1. This increase in the LIP index translates into improved customer satisfaction due to fewer cigarettes self-extinguishing during free burn conditions while maintaining reduced ignition propensity (e.g., self-extinguishing properties) when contacted with a substrate, thus improving the overall fire safety.

The data in FIG. 1 are based on commercial cigarette products using traditional starch band technology from dates ranging from 2005 to 2010. The average performance of the IP×FB index is 83±11%. In comparison, the embodiments of the present invention having wrappers comprising transition phase material, achieve a LIP index of 100% using different application methods to produce the LIP paper, i.e., (A) spraying the PTM aqueous suspensions at around room temperature, and (B) spraying and/or printing the hot melted PTM formulations. The total phase transition material concentration of the paper weight for Method A and Method B is 15% and 5%, respectively.

Without wishing to be bound by any scientific theory and explanation, applicants believe that three mechanisms give rise to the reduced IP effect demonstrated by the embodiments of the present invention comprising a wrapper with phase transition materials. First, the formation of a transient reduced gas permeability circumferential band comprising a melted wax barrier near the firecone. Second, the chemical inhibition of combustion. Third, the absorption of combustion heat by melting the phase transition material. Applicants believe that the primary mechanism responsible for the reduced IP effect is the creation of the transient reduced gas permeability circumferential band, which blocks the air flow to the burning firecone.

According to the present invention, the PTM particles distributed over the cigarette paper or other air-permeable membrane melt when subjected to the heat of the approaching cigarette firecone and clog or fill the pores of the cigarette paper. The clogged pores cause reduction of the air permeability of the cigarette paper to a level such that the contact of the cigarette with a substrate will cause a further reduction in the air permeability of the cigarette paper sufficient to suffocate the combustion zone, substantially reduce the intensity of smoldering of the cigarette firecone and extinguish it. This is considered to be a successful Ignition Propensity (IP) test. If the cigarette is freely suspended, i.e., it does not contact a substrate, the firecone will continue to receive a sufficient amount of air to support the free burn. This constitutes a successful Free Burn (FB) test. The product of these probabilities of successful passing both of these tests, i.e., IP×FB, is an overall LIP index, characterizing a cigarette capable of self-extinguishing when put on substrate, yet continuously burning in free air.

An illustrative example of the non-continuous, uniform manner in which the phase transition material is applied on the cigarette paper and the resulting air permeability (measured in Coresta units, or C.U.) as compared to the traditional, starch band technology is illustrated in FIG. 2A and 2B. As shown in FIG. 2B, cigarette papers manufactured with a starch based reduced IP technology typically have two circumferential bands of starch approximately 7 mm in length. The starch content is approximately 12-15% of the paper weight. In contrast, the embodiments of the present invention may comprise a non-continuous, uniform application of phase transition material which does not have large macro, discrete bands or regions on the paper. As illustrated in FIG. 2B, the phase transition material may be distributed on the surface as micro dots in a non-continuous manner. The phase transition material content may range between 2-35% of the paper weight.

Applicants have found that the air permeability of the prior art commercial fixed starch band reduced IP cigarettes decrease sharply form 20 C.U. to 5-7 C.U. in the starch band regions as shown in FIG. 2A. Conversely, embodiments of the present invention having a wrapper treated with a uniform, non-continuous application of phase transition material does not show a decrease in the air permeability for any region of the cigarette wrapper. Accordingly, in the embodiments of the present invention the air diffusion is not perturbed or restricted along the treated paper as compared to the fixed starch band regions of the prior art reduced IP cigarettes. Therefore, during smoking the overall diffusion characteristics of the paper are not altered versus untreated paper. Applicants believe that it is this feature that is primarily responsible for the excellent free burn properties observed for the embodiments of the present invention.

Another significant advantage of the present invention compared to the prior art fixed starch band reduced IP cigarettes is that the smoke content and, therefore, smoke taste and bio-activities stay constant throughout the tobacco column, and correspond to the continuously high air permeability paper. On the other hand, in the case of the fixed starch band reduced IP cigarettes the smoke content depends on the area, where puff is taken, i.e., the intake air travels mostly through the highly porous cigarette paper between bands, whereas within the dense starch band is redirected through the firecone. This may cause a difference in the content of the products of vaporization, combustion and pyrolysis of tobacco, and therefore in the smoke taste and bio-activity.

The primary mechanisms for achieving the reduced ignition propensity properties using PTMs according to the present invention are illustrated in FIG. 3A. Finely divided, or porous layers of PTM are distributed (optionally: uniformly, with concentration gradients, in the form of bands or clusters, singular or plural) and affixed on the paper. The PTMs are chosen based on their physico-chemical properties, such as melting temperature, heat of fusion, and can be mixtures of polar, non-polar, hydrophilic or hydrophobic, homogeneous or heterogeneous wax mixtures or individual components. The waxes can be applied to the paper in a homogeneous or heterogeneous fashion. The waxes subsequently melt when exposed to the elevated temperatures achieved on smoking articles in the vicinity of approaching firecone. Once the PTM has transitioned from solid to a liquid state when subjected to the temperature generated by the burning firecone, it will wick primarily radially. As the PTM wicks, it forms a non-porous band, which reduces the air supply to firecone, thus suppressing combustion to a complete stop once the article is in contact with a solid surface for an extended period of time. The formation of the reduced gas permeability or reduced porosity circumferential band is referred to herein as the “Transient Band” as it is only formed during smoking ahead of the firecone. This band is dynamic and not fixed, such that it continuously moves ahead the firecone. The rate and extension of the wicking process is governed by the nature of the paper and PTMs and their interactions. Proper selection of the PTMs and application method dramatically impact the speed at which the Transient Band is formed and subsequently the speed at which the smoking article will extinguish.

Alternatively, it will be understood that the PTM may be applied to discrete regions (such as individual or pluralities of zones or bands) of the cigarette paper while leaving some areas untreated. This approach may create air permeability/porosity gradients as well as randomly distributed zones of various air permeability/porosity.

FIG. 3B further illustrates the PTMs capability to reduce the air permeability of the base paper. The relationship between concentration of PTM and reduction in air permeability after thermal treatment at 100° C. for 10 minutes demonstrates the effectiveness of the transient band to reduce air flow through the cigarette paper.

Without wishing to be bound by any scientific theory and explanation, applicants believe that the physico-chemical properties of the paper substrate, including the micro porosity and total pore volume, are related to the ability to achieve ignition propensity. FIG. 4A shows the pore size distribution of 19 C.U. and 32 C.U. cigarette papers treated with approximately 12% wax. FIG. 4B shows the same cigarette papers thermally treated at 130° C. for 10 minutes. The data indicate a significant reduction in the total pore volume of the approximately 0.5-1 μm pore sizes when sufficient PTM is applied to the paper and is subsequently thermally treated. This confirms the liquid PTM wicks into the pores upon melting. Furthermore, FIGS. 5A and 5B shows the reduction in pore volume as a function of wax content on 19 C.U. paper pre and post thermal treatment, respectively. The abrupt change in the pore volume of the paper treated with 5% wax corresponds to a 100% reduction of ignition propensity of the cigarette. This behavior can be explained using percolation theory. That is to say, once approximately 60% of the pore volume has been occupied by the liquid PTM, sufficient reduction in air diffusion is achieved to impart ignition propensity.

FIG. 5A shows the effect of PTM concentration on the paper on the total pore volume of the 0.5 um and 5.0 μm pores as measured by mercury porosimetry. FIG. 5B shows the reduction in the same pore size regimes post thermal treatment. The onset of 100% reduction of ignition propensity occurs at 5% PTM concentration on the papers.

It has also determined that the mechanism of LIP can be optionally augmented by inhibiting combustion when using PTMs that possess the fire retardant properties, i.e., ethylene-bis-stearamide, other amides, phosphor, sulfur and other hetero-organic compounds, inorganic salts and oxides of alkali and alkali-earth metals, and some types of activated carbons with such properties are used. It has been found that the third mechanism, or absorbing heat of burning firecone, promotes LIP performance in the cases of heavy loadings of PTM in paper and/or using PTMs with the heat of fusion at the level of approximately 200 Joules per gram and higher.

Applicants have found that the time required for a cigarette to self-extinguish (i.e., the LIP effect speed) is dramatically reduced with cigarettes having wrappers embodying the present invention. This LIP effect speed can be quantified by the length of the cigarette that is burned before it self-extinguishes. As shown in FIG. 7, for example, cigarettes having 19 C.U. and 32 C.U. wrappers treated with PTM according to the present invention self-extinguish after about 5 mm of the length of the cigarette has burned. In contrast, about 25 mm length of the commercial LIP starch band cigarettes burned before it self-extinguished. Cigarettes embodying the present invention with wrappers having different porosities demonstrate similar improved LIP effect speed.

Applicants have further found that cigarettes embodying the present invention demonstrate much lower LIP effect speed variability. As shown by the standard deviations of the length of burn before self-extinguishing in FIG. 7, cigarettes embodying the present invention have a LIP effect speed variability of approximately 7 mm, as opposed to 30 mm for commercial LIP fixed starch band cigarettes. In other words, cigarettes embodying the present invention have the additional benefit of self-extinguishing within a more uniform length of cigarette burn than the prior art LIP fixed starch band cigarettes.

With reference to FIG. 8, applicants have found that an increase in the concentration of PTM in the vicinity of 5% results in an abrupt decrease in the ˜1 μm paper pore volume. This is accompanied by an onset of the LIP property of a cigarette constructed with such a wrapper. The result demonstrates that the paper pores, filled with PTM to an extent of about 60%, cause quick development of LIP property, obeying therefore the bond percolation theory. Applicants have further found that the rate of development of the transient band and its dynamic follow the Washburn equation:

Lucas-Washburn's Equation

L2/t=[γ*R*cos(Θ)]/[2*η],

where the advance of capillary flow L through the pore of radius R over time t.

L depends on viscosity η, surface tension γ of liquid wax formulation and the time-dependent contact angle Θ between its meniscus and the capillary wall.

Even though the PTMs are defined as wax-type hydrocarbons or esters of fatty acids that are insoluble in water but soluble in non-polar organic solvents, the present invention includes water soluble and dispersible wax materials. By appropriately choosing a combination of two or more different waxes, the diffusion (wicking) of the liquefied PTM near the firecone from inner to the outer surface of cigarette paper can be controlled. Applicants discovered that excessive wicking may be detrimental to the cigarette appearance, and can be minimized or eliminated by using PTMs with specific combinations of physical properties, including but not limited with hydrophobicity, hydrophilicity, heat of fusion and melting temperatures.

The present invention has been found to work successfully for several paper types with air permeabilities from 19 to 100 C.U., when the PTM formulations applied by melted spray or printed using ink jet technology on paper surface.

The ability to manipulate and control the porosity and gas diffusivity through the paper to introduce the LIP property by deposition of a uniform, non-continuous coating is done in a variety of methods of deposition of variety of PTM formulations. Such deposition could be done in a form of patterns that are appropriate for desired paper air permeability and porosity and could be created in a manner that allows selective tuning of the surface morphology and composition of papers from different and independent suppliers. Therefore, the present invention leads to the reduction of impact of paper variability on the LIP index, so that the air permeability and porosity of any base paper could be changed at will to meet requirement of cigarette product architecture.

The present invention simplifies the practice and reduces the costs of LIP cigarette production by depositing or applying the PTM on-line at a cigarette making machine. The phase transition compositions can be formulated for other applications and improved appearance of the transient band in all parts, i.e., the low-temperature zone firecone, char line and ash boundary of a lit cigarette, in flavor delivery and in the LIP performance at a minimal content of PTMs.

The present invention may further involve a digitally-assisted deposition of the phase transition material by the known technologies such as spraying of PTM dispersions, inkjet printing, or other standing printing technologies with the capability of applying the uniform, non-continuous coatings and/or layers of material on cigarette paper.

An improved manufacturing robustness of the new technology to produce LIP paper has been achieved performing deposition of PTMs on paper by variety of spraying and printing techniques, which include but not limited with the gravure and flexography. A high speed deposition technique enables printing on paper surfaces that have a broad range of surface chemistries and variable porosities. Therefore, the discovered LIP mechanisms in conjunction with the well-controlled digital deposition can accommodate lot-to-lot variations in properties of papers from different manufacturers, without compromising the both LIP and smoke performances. 

1. A method of imparting reduced ignition propensity to a smoking article comprising a tobacco column and a wrapper surrounding the tobacco column and having a porous structure with a base permeability, the method comprising: (a) treating the wrapper with a phase transition substance which, upon being exposed to the heat produced by a burning firecone of the tobacco column, at least partially fills the wrapper porous structure in the vicinity of the burning firecone to form an area of the wrapper having a reduced permeability that is lower than the wrapper base permeability; wherein the reduced permeability of the wrapper in the vicinity of the firecone permits sufficient air flow through the wrapper to sustain free burn, but, when the smoking article is placed on a substrate, the reduced permeability of the wrapper in the vicinity of the wrapper imparts reduced ignition propensity such that there is insufficient air flow to sustain combustion of the firecone or insufficient air flow to sustain an intensity of the burning firecone necessary to ignite the substrate.
 2. The method according to claim 1, wherein an inner surface of the smoking article wrapper which contacts the tobacco column is treated with the phase transition substance.
 3. The method according to claim 1, wherein an exterior surface of the smoking article wrapper is treated with the phase transition substance.
 4. The method according to claim 1, wherein the phase transition substance is embedded in the wrapper pore structure.
 5. The method according to claim 1, wherein the phase transition substance, upon being subjected to the heat produced by a burning firecone of the tobacco column, changes from a solid phase to a liquid phase and wicks into the wrapper pore structure in the vicinity of the burning firecone to at least partially fill the wrapper porous structure in the vicinity of the burning firecone and form an area of the wrapper having a reduced permeability that is lower than the wrapper base permeability.
 6. The method according to claim 1, wherein the phase transition substance is selected from the group consisting of paraffin, tobacco wax, Solanesol, carnauba, Beeswax, microcrystalline wax or combinations thereof.
 7. The method according to claim 6, wherein the phase transition substance further comprises a liquid crystal substance.
 8. The method according to claim 1, wherein the wrapper comprises a cellulosic fiber web having a base porosity of between about 10 and 100 Coresta Units.
 9. The method according to claim 1, wherein substantially the entire wrapper is treated with a non-continuous application of the phase transition substance.
 10. The method according to claim 9, wherein the non-continuous application of the phase transition substance comprises a substantially uniform pattern.
 11. The method according to claim 9, wherein the non-continuous application of the phase transition substance comprises a substantially random configuration.
 12. The method according to claim 1, wherein a population of the smoking articles exhibits a LIP index defined as the product of the free burn success rate and the ignition propensity success rate that exceeds about 90%.
 13. The method according to claim 12, wherein the population of smoking articles is at least about 10 smoking articles.
 14. The method according to claim 12, wherein the population of smoking articles is between about 20 and 40 smoking articles.
 15. The method according to claim 12, wherein the LIP index of the population of smoking articles is substantially 100%.
 16. The method according to claim 15, wherein the population of smoking articles is at least about 10 smoking articles.
 17. The method according to claim 15, wherein the population of smoking articles is between about 20 and 40 smoking articles.
 18. The method according to claim 1, wherein the area of the wrapper having a reduced permeability comprises a circumferential band proximal the wrapper charline adjacent the firecone.
 19. The method according to claim 1, wherein the wrapper is treated with an effective amount of the phase transition substance such that the base porosity of the wrapper is not substantially altered by the phase transition substance at room temperature.
 20. A method of imparting reduced ignition propensity to a smoking article comprising a tobacco column and a wrapper surrounding the tobacco column and having a porous structure with a base permeability, the method comprising: (a) treating the wrapper with a phase transition substance which, when subjected to an intensive variable resulting from combustion of the burning firecone of the tobacco column, undergoes a physical transformation and at least partially fills the wrapper porous structure in the vicinity of the burning firecone to form an area of the wrapper having a reduced permeability that is lower than the wrapper base permeability; wherein the reduced permeability of the wrapper in the vicinity of the firecone permits sufficient air flow through the wrapper to sustain free burn, but, when the smoking article is placed on a substrate, the reduced permeability of the wrapper in the vicinity of the wrapper imparts reduced ignition propensity such that there is insufficient air flow to sustain combustion of the firecone or insufficient air flow to sustain an intensity of the burning firecone necessary to ignite the substrate. 